Spark plug



FIG. 1 is a front, top and side perspective view of the spark plugembodying the design of the present invention;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a side elevational view thereof, the opposite side elevationalview being identical thereto;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The ornamental design for a spark plug, as shown and described.